The present invention relates generally to devices and methods for promoting blood circulation to the heart muscle. More particularly, the present invention relates to devices and methods for forming holes, craters or channels in the interior walls of a heart chamber as part of a percutaneous myocardial revascularization (PMR) procedure.
Assuring that the heart muscle is adequately supplied with oxygen is critical to sustaining the life of a patient. To receive an adequate supply of oxygen, the heart muscle must be well perfused with blood. In a healthy heart, blood perfusion is accomplished with a system of blood vessels and capillaries. However, it is common for the blood vessels to become occluded (blocked) or stenotic (narrowed). A stenosis may be formed by an atheroma which is typically a hard, calcified substance which forms on the walls of a blood vessel.
Historically, individual stenotic lesions have been treated with a number of medical procedures including coronary bypass surgery, angioplasty, and atherectomy. Coronary bypass surgery typically involves utilizing vascular tissue from another part of the patient""s body to construct a shunt around the obstructed vessel. Angioplasty techniques such as percutaneous transluminal angioplasty (PTA) and percutaneous transluminal coronary angioplasty (PTCA) are relatively non-invasive methods of treating a stenotic lesion. These angioplasty techniques typically involve the use of a guidewire and a balloon catheter. In these procedures, a balloon catheter is advanced over a guidewire such that the balloon is positioned proximate a restriction in a diseased vessel. The balloon is then inflated and the restriction in the vessel is opened. A third technique which may be used to treat a stenotic lesion is atherectomy. During an atherectomy procedure, the stenotic lesion is mechanically cut or abraded away from the blood vessel wall.
Coronary by-pass, angioplasty, and atherectomy procedures have all been found effective in treating individual stenotic lesions in relatively large blood vessels. However, the heart muscle is perfused with blood through a network of small vessels and capillaries. In some cases, a large number of stenotic lesions may occur in a large number of locations throughout this network of small blood vessels and capillaries. The torturous path and small diameter of these blood vessels limit access to the stenotic lesions. The sheer number and small size of these stenotic lesions make techniques such as cardiovascular by-pass surgery, angioplasty, and atherectomy impractical
When techniques which treat individual lesion are not practical a technique known as percutaneous myocardial revascularization (PMR) may be used to improve the oxygenation of the myocardial tissue. A PMR procedure generally involves the creation of holes, craters or channels directly into the myocardium of the heart. PMR was inspired in part by observations that reptilian heart muscles are supplied with oxygen primarily by blood perfusing directly from within heart chambers to the heart muscle. This contrasts with the human heart, which is supplied by coronary vessels receiving blood from the aorta. Positive clinical results have been demonstrated in human patients receiving PMR treatments. These results are believed to be caused in part by blood flowing within a heart chamber through channels in myocardial tissue formed by PMR. Increased blood flow to the myocardium is also believed to be caused in part by the healing response to wound formation. Specifically, the formation of new blood vessels is believed to occur in response to the newly created wound. This response is sometimes referred to as angiogenisis.
In addition to promoting increased blood flow, PMR may also improve the condition of a patient through denervation. Denervation is the elimination of nerve endings. Wounds created during PMR result in the elimination of nerve endings which were previously sending pain signals to the brain as a result of hibernating tissue. In one embodiment in accordance with the present invention, a fluid under pressure is forced into the wound formed by PMR. This fluid may include saline, contrast media, a therapeutic agent, a caustic agent, or any combination of these. Means for detecting contact 706 may be used to verify that electrode 30 is in contact with myocardial tissue when the fluid is delivered. Injecting a fluid including a radiopaque contrast media creates a radiopaque marker of the treatment site. Injecting a fluid including a therapeutic agent into the wound may enhance the angiogenic response of the body. Forcing fluid under pressure into the wound may also create collateral damage within an area proximate the wound. This collateral damage may include the rupturing of blood vessels, capillaries, and sinuses within the myocardium. This collateral damage will increase the healing response by angiogenisis.
A number of methods have been used to create channels in the myocardium during percutaneous myocardial revascularization. Methods of cutting include the use of knife-like cutting tools and cutting with light from a LASER. Radio frequency energy may also be used to burn or ablate channels or craters into myocardial tissue.
The present invention relates to methods and devices for performing percutaneous myocardial revascularization without interfering with the blood pumping activity of the heart. A desirable feature of the present invention is that the delivery of radio frequency energy to an area proximate the heart is discontinued when the heart is in a vulnerable period of the cardiac rhythm. A second desirable feature of the present invention is that the discharge of electrical energy stored in the heart is disallowed during vulnerable periods of each heart beat.
A system for performing percutaneous myocardial revascularization in accordance with the present invention typically includes an active electrode disposed at the end of a catheter, and a radio frequency generator coupled to the active electrode. The PMR system further includes a means for patient monitoring capable of detecting electrical activity in the heart of a patient. Radio frequency energy is selectively applied to the active electrode only when the heart is not in a vulnerable stage of the cardiac rhythm.
Embodiments of a percutaneous myocardial revascularization system in accordance with the present invention may also include provisions to assure that the active electrode is properly positioned. In one embodiment of the present invention an impedance means is coupled between the active electrode and the radio frequency generator. The impedance value of the impedance means is selected so that maximum power transfer will occur when the active electrode is in contact with the myocardial tissue of the patient""s heart. To accomplish this, the impedance value of the impedance means is selected so that the impedance of the PMR system is substantially equal to the load impedance which will be encountered by the system when the active electrode contacts the myocardial tissue of the patient""s heart.
An additional embodiment of the present invention includes a means for detecting contact between the active electrode and the myocardial tissue of a patient""s heart. This embodiment is for use with a method of PMR during which a high level of radio frequency energy is not applied to the active electrode until contact between the active electrode and myocardial tissue has been detected. A relatively low level of radio frequency energy is utilized to detect contact between the active electrode and myocardial tissue. A high level of radio frequency energy is selectively applied to the active electrode only after contact has been verified.
A method in accordance with the present invention avoids discharging high levels of radio frequency energy into the blood. The discharge of high levels of radio frequency energy into the blood may cause complications such as platelet damage, gas bubbles, and blood clots.